The invention is a bone distractor apparatus used during osteotomy procedures wherein a bone, such as the mandible for example, is to be lengthened by separating the bone into two segments, allowing bone regeneration to begin within the osteotomy gap, then slowly expanding the gap incrementally over time such that the bone is gradually extended to its desired length and the gap is completely filled with regenerated bone, a process referred to as osteogenesis or osteosynthesis. The bone distractor is a generally elongated device that comprises a mechanism, such as a threaded rod contained within a tubular housing, the rod being in connection with one or two movable shoe or mounting bracket members to which are connected a proximal bone plate and a distal bone plate, whereby the bone plates affixed on either side of the osteotomy gap to the bone to be extended can be gradually separated in a controlled and precise manner by rotating the threaded rod.
Often the distractor and mounting brackets are composed of metal, while the bone plates and bone screws are composed of a resorbable material, such that they will degrade and decompose within the body such that removal is not required. Because the distractor and mounting brackets often will not be removed until the bone plates and bone screws have seriously degraded, it is possible to remove and extract the distractor and mounting brackets from the patient by tearing the metal components from the resorbable components, which is accomplished by pulling the distractor generally in the axial direction through the surrounding tissue.
In an embodiment of interest, the metal mounting brackets are provided with abutment members that extend generally perpendicularly to the major plane containing the bone plates, such that the abutment members can be positioned against the ends of the bone segments which were created by the osteotomy. The abutment members provide a means to transfer the distraction force to the bone segments in addition to the bone screws that secure the bone plates to the bones, which is particularly desirable as the resorbable bone screws and bone plates weaken over time. Typically, the abutment members comprise relatively short arm or hook members.
The presence of these abutment members means alters slightly the technique for removing the distractor and the mounting brackets, since the distractor must now first be pulled slightly away from the bone segments or levered using the distal end as a fulcrum in a direction generally perpendicular to the axial direction in order for the abutment members to clear the bone during the axial extraction step. The abutment members, extending generally perpendicularly to the axial direction, increase damage to the tissue surrounding the distractor and mounting plates when withdrawn in the axial direction, especially for the abutment member on the distal bone plate, which is more difficult to access and manipulate during the extraction process.
It is an object of this invention to address the problems created during the distractor extraction process by the generally perpendicular abutment members, and in particular the distal abutment member, by structuring at least the distal member such that it is able to collapse in the distal direction so as to lie adjacent the mounting bracket or at least present a much reduced profile in the axial direction, whereby damage to the tissue surrounding the distractor and mounting bracket or brackets is significantly reduced when the distractor is pulled in the generally axial direction during removal.